This invention relates generally to a butterfly valve for application within a fluid flow passageway, and more particularly, to a lapping sleeve device for protecting the valve disc element and its pivot stem from corrosion.
Butterfly valves are frequently used in fluid flow lines where it is desired to load or unload fluid materials for shipment or storage. Such uses include tank trailers for transporting fluids from one location to another, as well as fluid flow lines for loading and unloading tank trailers, barges, ships or other means of transportation and storage. The typical butterfly valve customarily uses a pivotally mounted disc-type valve in a flow line which also incorporates a resilient seal against which the disc valve pivots to seal off the flow line, and when opened, to allow fluid materials to be conveyed along the flow line. Examples of butterfly valves are included in my prior U.S. Pat. No. 4,822,001.
The substances transported in tanks using butterfly valves are often caustic or acidic. When these caustic materials enter the valve pivot stem pivot apertures, they can corrode the valve seat and pivot stem. This corrosion diminishes the effectiveness of the resilient seal within the valve causing leakage. Several attempts have been made in the prior art to manufacture butterfly valves that resist corrosion. For example, the inner wall of the flow chamber is sometimes protected with a chemically resistant material. Although this protects a portion of the stem hole or aperture and resist corrosion, the pivot stem and disc element pivot seat areas are still exposed to the caustic or acidic materials which leads to corrosion and an ineffective valve.